The long-term objective of this proposal is to generate knowledge that may be used to prepare for or prevent pandemic influenza. The interspecies transmission of influenza viruses is a key element in the generation of a pandemic influenza strain. Although little is known about the molecular steps required to create a potential human pandemic strain, intermediate hosts are considered necessary. Aquatic birds are the natural reservoir of influenza A viruses, but the influenza A viruses isolated from humans in Hong Kong (H5N1 in 1997 and H9N2 in1999) contained genes that had circulated and adapted in land-based birds, particularly quail, which are widely farmed in Southern China. Epidemiological evidence and our preliminary results strongly suggest that quail could play a unique role among land-based birds in the emergence of novel influenza A viruses that can cross the species barrier. The proposed research will use molecular, classical virologic, and reverse genetics methods to define 1) the role of land-based birds, particularly quail, as intermediate hosts in interspecies transmission and spread of influenza A viruses; and 2) the molecular basis of the transmissibility of influenza A viruses in land-based avian intermediate hosts. With poultry production increasing worldwide (more than 200% since the 1960's), the mechanisms underlying interspecies transmission of influenza viruses must be elucidated if the emergence of a pandemic influenza strain is to be forestalled or adequately prepared for. The techniques needed to obtain this information are now available, and the results will lay the groundwork for important changes in agricultural policies and pandemic planning.